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Ultracold Quantum Gases Group

Welcome to the ultracold quantum gas research group at Aarhus University!

In our research we investigate the properties of atomic gases at extremely low temperatures. This allows us to understand the fundamental quantum mechanical behaviour of few- and many-particle systems.


Evaporation and probing procedure to determine the BEC transition

Measurement-enhanced determination of BEC phase diagrams

Shot-to-shot fluctuations plague many experiments within the field of quantum gases. The HiRes lab have demonstrated how dispersive atom number measurements during evaporative cooling can be used for enhanced determination of the non-linear parameter dependence of the transition to a Bose-Einstein condensate (BEC).

You can read the first experimental paper from the HiRes lab on arXiv. (07/2016)

Phases of two interacting BECs

Phase Separation and Dynamics of two-component Bose-Einstein condensates

The miscibility of two interacting quantum systems is an important testing ground for the understanding of complex quantum systems. Two-component Bose-Einstein condensates enable the investigation of this scenario in a particularly well controlled setting. In a homogeneous system, the transition between mixed and separated phases is characterised by a 'miscibility parameter'. In this theoretical analysis we have shown that this parameter is no longer the optimal one for trapped gases, for which the location of the phase boundary depends critically on atom numbers.

The manuscript has been published in Physical Review A and is also available on arXiv. (07/2016)

Setup of the FPGA-based laser locking system

A simple laser locking system based on a field-programmable gate array

Modern quantum gas labs require a number of laser systems which are typically difficult to construct or expensive to buy commercially. We have developed a laser frequency stabilization system based on a field-programmable gate array, with emphasis on hardware simplicity, which offers a user-friendly alternative to commercial and previous home-built solutions. Frequency modulation, lock-in detection and a proportional-integral-derivative controller are programmed on the field-programmable gate array and only minimal additional components are required to frequency stabilize a laser. The locking system is administered via LabVIEW from a host-computer which provides comprehensive, long-distance control through a versatile interface. The source code is available online.

The manuscript has been accepted for publication in Review of Scientific Instruments and is currently available on arXiv. (07/2016)

Coupled interferometer states in a Rb BEC

0.75 atoms improve the clock signal of 10,000 atoms

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology. In a classical interferometer, atoms are prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). We have experimentally demonstrated a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. http://arxiv.org/abs/1605.07754 (05/2016)

Polaron spectrum in a Bose-Einstein condensate

Observation of attractive and repulsive polarons in a Bose-Einstein condensate

The behavior of a mobile impurity particle interacting with a quantum-mechanical medium is of fundamental importance in physics. Our understanding of the impurity problem has improved dramatically since it was realized experimentally using degenerate Fermi gases. However, there has not been such a realization of the impurity problem in a bosonic reservoir so far. Here, we use radio frequency spectroscopy of ultracold bosonic 39K atoms to experimentally demonstrate the existence of a well-defined quasiparticle state for an impurity interacting with a Bose-Einstein condensate. http://arxiv.org/abs/1604.07883 (04/2016)

Experimental sequence and schematic of
the key elements of the experiment.

Preparation of ultracold atom clouds at the shot noise level

We prepare number stabilized ultracold clouds through the real-time analysis of non-destructive images and the application of feedback. In our experiments, the atom number N∼10^6 is determined by high precision Faraday imaging with uncertainty ΔN below the shot noise level, i.e., ΔN<√N. Based on this measurement, feedback is applied to reduce the atom number to a user-defined target, whereupon a second imaging series probes the number stabilized cloud. By this method, we show that the atom number in ultracold clouds can be prepared below the shot noise level. http://arxiv.org/abs/1604.05087 (04/2016)

Three-body recombination in KRb mixtures displays a surprising lack of Efimov physics

Absence of observable Efimov resonances in ultracold KRb mixtures

Ultracold atomic gases have recently become a driving force in few-body physics due to the observation of the Efimov effect. In previous experiments with ultracold mixtures of potassium and rubidium, an unexpected non-universal behavior of Efimov resonances was observed. We have measured the scattering length dependent three-body recombination coefficient in ultracold heteronuclear mixtures of 39K-87Rb and 41K-87Rb and do not observe any signatures of Efimov resonances. This reestablishes universality of the three-body parameter across isotopic mixtures. http://arxiv.org/abs/1604.03693 (04/2016)

Research receives attention in popular media

Recently, an international collaboration including Jan Arlt published an article in Nature Communications: Satisfying the Einstein–Podolsky–Rosen criterion with massive particles

Two popular articles were written in danish based on this research:

Den havde Einstein ikke set komme (Einstein didn't see that coming)

Ny fysisk metode bruges til at lave afsindigt præcise målinger (New method in physics allows incredibly precise measurements)


Jan Arlt

New grant: Experiments with Quantum Test Beds

Jan Arlt has recieved a grant from VILLUM FONDEN valued at DKK 4.7 million. View more details here. (01/2016)


The Villum Foundation